This invention relates to an imaging apparatus and method utilizing nuclear magnetic resonance (abbreviated hereinafter as NMR) for imaging, and more particularly to an imaging apparatus of the kind described above which is suitable for imaging a moving region of an object with high accuracy.
In an imaging apparatus utilizing the phenomenon of NMR, echo signals from various positions of an object must be separated and discriminated from one another. According to one of methods employed hitherto, a field gradient is applied to a magnetic field in which an object is placed, and different resonance frequencies or phase encoding amounts are based to derive position information. Such a method is described in, for example, U.S. Pat. No. 4,506,222. In the method described in this U.S. patent, excitation and measurement of a plurality of NMR signals derived from a living body in response to application of phase-encoding field gradients having different amplitudes are required so as to obtain one tomographic image. Therefore, the total length of time required for the measurement becomes necessarily long as compared to the cardiac cycle in the living body.
On the other hand, a gated imaging method is also known which is proposed to prevent blurring of an image due to the cardiac action or breathing of a living body. For example, a technique of gated imaging in X-rays computer tomography is described in U.S. Pat. No. 3,952,201. Also, JP-A-62-4423l (1987) proposes a method of cardiac action or breathing gated imaging in an NMR imaging apparatus. In these publications, the cardiac action was indirectly measured by means of electric cardiography.